Date of Award

5-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Danlin Yu

Committee Member

Clement Alo

Committee Member

Jill Lipoti

Committee Member

Stefan Robila

Abstract

Intensive horticulture production has broad environmental implications due to the high dependency on natural resources. Numerous reports indicate positive socio-economic gains associated with the Kenyan horticulture sub-sector. Even so, few highlight the extent of the negative environmental impacts. We adopt a holistic approach that integrates deskwork, Geographical Information Systems (GIS), field study and remote sensing tools to evaluate the spread and growth of commercial horticulture, and the effects on: i) surface water quality, and ii) vegetation condition, in watersheds experiencing increased production within the central highlands. The desk research utilized Google Earth archives and GIS data, to map greenhouse distribution, determining area under production and factors predicting choice of location. This was followed by a field study to sample and characterize surface water quality in select sub-watersheds with intensive horticulture, thereby highlighting potential pollutant source-processes. Twenty five years of remote sensing data were also analyzed to establish vegetation condition and responses to increased farming and human disturbances. This was followed by a detailed study to quantify land use and land cover changes, and finally a chapter illustrating trends in horticulture exports volumes. Results from the desk research showed heterogeneous spread of farming, where area under production increased rapidly between 2000 and 2011. Population density, average slope, average rainfall and dams were significant predictors to farming location. Results from the field study show predominance of anthropogenic trace elements of cadmium, phosphate, and zinc in waters draining from regions with intensive large scale horticulture. The long-term vegetation study indicates spatially varying inter-annual NDVI, which continuously declined post 1990s in sub watersheds with increased farming. The study to quantify land transformation dynamics, indicate varying magnitudes of change with rates of change differing between land-uses, and between case studies, attributable to socio-economic drivers. We also find that horticultural exports had positive trends until 2008/2009, and 2010, where the effects of post-election violence and volcanic eruption are evident. Overall, the research has demonstrated the efficacy of integrated approaches in understanding implications intensified production on watershed resources. This knowledge is important in developing policies and regulatory frameworks that supports sustainable resource utilization and best management practices.

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